NR: Design and Evaluation of Retrieval Functions in Peer-to-Peer File Sharing Systems

点对点（P2P）文件共享系统允许在分布式终端系统或对等体之间共享内容。文件存储在对等体上，并在它们之间直接传输。在过去的几年里，这种系统的普及程度大大提高。除了最近的流行之外，点对点系统代表了一种重要的新内容交付范式，从长远来看，它有可能重新塑造互联网的体系结构和性能。典型的P2P用户会话包括一个搜索阶段，其中可以执行多个搜索，然后是一个检索阶段，其中可以请求多个文件。为了提高性能和健壮性，许多研究和开发已经投入到不同的文件搜索系统的设计中。在本文的工作中，研究人员将重点放在文件检索阶段，这一阶段迄今为止受到学术界的关注较少。我们的动机来自三个主要观察：(i) P2P系统的用户体验是搜索和检索功能性能的总和；（ii）检索阶段使用的网络资源可能远远超过搜索阶段消耗的资源。因此，检索阶段设计的新范式和改进可以对互联网的总体性能产生深远的影响；（iii） P2P系统为内容检索提供了与更传统的客户端-服务器模型明显不同的上下文；它们具有更大规模的内容复制，可能具有严重的资源约束，并且具有很强的动态性。我们建议的研究包括三个方面：1。改进检索阶段性能的对等选择策略。研究人员研究了这个问题的两个方面，这两个方面是P2P环境所特有的，并且很少受到关注：(i)由于P2P系统中固有的大规模复制，搜索阶段只能发现可用副本的子集，以及（ii）服务对等体的约束性质，这可能需要请求阻塞，直到服务容量可用。同时涉及多个服务节点的内容检索策略。P2P系统中可能存在的大规模复制导致了从多个对等点并行执行文件检索的有趣可能性，这既提高了性能，又克服了对等点的动态和不稳定性。这项工作考虑了大规模部署并行下载对性能的影响以及网络用户之间的公平性。此外，我们的工作在这种背景下重新审视了选择问题。一个整体的方法来操作P2P系统。目标是改善P2P用户的整体搜索和检索体验。我们引入了一个新的维度，即搜索质量，通过它可以判断搜索阶段结果的性能及其对检索阶段性能的影响。研究人员以这种新的视角研究了现有的搜索技术，并考虑了两种搜索范式，这些范式受到先前在分布式匹配算法和广播流调度方面的工作的启发。研究成果将包括上述领域的理论和实践研究。研究人员将使用各种技术来评估我们的想法（包括数学和理论分析，模拟，仿真和实验）。这项工作将是第一个深入研究P2P系统中检索阶段的工作。由于网络资源的使用主要受检索阶段需求的影响，这项工作也将为理解P2P系统对互联网资源的影响提供基础，并进一步指导提供工作以满足P2P系统的需求。我们还致力于促进拟议工作的更广泛影响的活动，包括：(i)根据我们的研究生和本科生研究开发模块，（ii）继续强调在我们的研究工作中纳入代表性不足的群体，以及（iii）向亚特兰大历史悠久的黑人学院和大学开展外展活动。

Peer-to-peer (P2P) file sharing systems allow content to be shared between distributed end-systems or peers. Files are stored at the peers and transferred directly between them. The last few years have seen the popularity of such systems grow tremendously. Beyond their recent popularity, peer-to-peer systems represent a significant new content delivery paradigm that has the potential to re-shape the architecture and performance of the Internet in the long term. A typical P2P user session consists of a search phase where multiple searches may be conducted followed by a retrieval phase in which multiple files may be requested. Much research and development has gone into the design of differing systems for file search, with the aim of improving performance and robustness. In the proposed work, the researchers focus on the file retrieval phase, which has so far received less attention from the research community. We are motivated by three main observations: (i) A P2P system user's experience is the sum total of the performance of both the search as well as the retrieval functions; (ii) The network resources used during the retrieval phase can outweigh by far the resources consumed during the search phase. As such, new paradigms and improvements in the design of the retrieval phase can have far reaching implications on the performance of the Internet in general; (iii) A P2P system provides a significantly different context for content retrieval than the more traditional client-server model; they have larger scale content replication, the peers may possess severe resource constraints, and the peers are quite dynamic. Our proposed research encompasses three areas:1. Peer selection strategies for improved performance of the retrieval phase. The resesearchers examine two aspects of this problem that are unique to the P2P environment and that have received little attention: (i) the fact that, due to the large-scale replication inherent in P2P systems, the search phase can only discover a subset of available replicas, and (ii) the constrained nature of serving peers which may require requests to block until serving capacity is available.2. Content retrieval strategies involving multiple serving peers simultaneously. The large scale replication that may be present in P2P systems leads to the interesting possibility of performing file retrieval from multiple peers in parallel, both to improve performance and overcome peer dynamics and instability. This work considers the effect of wide-scale deployment of parallel downloading on performance as well as fairness among network users. In addition, our work revisits the selection problem in this context.3. A holistic approach to the operation of P2P systems. The objective is to improve overall P2P user search and retrieval experience. We introduce a new dimension, the quality of a search, by which one should judge the performance of the outcome of a search phase and its effect on the performance during the retrieval phase. The researchers study existing search techniques with this new perspective and also consider two search paradigms inspired by prior work on distributed match-making algorithms and broadcast-stream scheduling.The research output will consist of theoretical as well as practical studies of the areas described above. THe researchers will use a variety of techniques to evaluate our ideas (including mathematical and theoretical analysis, simulation, emulation, and experimentation). This work will be among the first to study the retrieval phase in P2P systems in depth. Because network resource usage is primarily influenced by the retrieval phase requirements, this work will also provide the basis of an understanding of the effect of P2P systems on Internet resources and further guide provisioning efforts to meet the demands of P2P systems. We are also committed to activities that will promote the broader impact of the proposed work including: (i) development of modules based on our research for graduate and undergraduate classes, (ii) continued emphasis on inclusion of under-represented groups within our research efforts and (iii) outreach activities to Atlanta-based historically black colleges and universities.